Apparatus for determining location of bubbles in tubes in level instruments



April 15, 1952 2,592,941

W. D. MOORE APPARATUS FOR DETERMINING LOCATION OF BUBBLES IN TUBES IN LEVEL INSTRUMENTS Filed Sept. 3, 1949 4 Sheets-Sheet l 3nnentor (Ittornegs April 15, 1952 w D MOORE 2,592,941

APPARATUS FOR DETERMINING LOCATION OF BUBBLES IN TUBES IN LEVEL INSTRUMENTS Filed Sept. 3, 1949 4 Sheets-Shet 2 fl4///4/27 Q Waare 71ZAMhM attorney 5 Aprll 15, 1952 w. D. MOORE 2,592,941

APPARATUS FOR DETERMINING LOCATION OF BUBBLES IN TUBES IN LEVEL INSTRUMENTS Filed Sept. 3, 1949 4 Sheets-Sheet 5 Bnventor Qttornegs April 15, 1952 w. D. MOORE 2,592,941

' APPARATUS FOR DETERMINING LOCATION OF BUBBLES IN TUBES IN LEVEL INSTRUMENTS Filed Sept. 3, 1949 4 Sheets-Sheet 4 (Ittomegs Enventpr Patented Apr. 15, 1952 .U NITED STATES PATENT OFFICE APPARATUS FOR DETERMINING LOCATION 'OF BUBBLES IN TUBES IN LEVEL INSTRU- MENTS William D. Moore, -Kansas City, 'Mo., assignorto Brunson :Instrument Company, 1Inc., -Kansas City, Mo., a corporation 'of Missouri Application September 3, 1949, Serial No. 114,043

and/or level conditions, and more particularly to 5 1 such an instrument in which therelative position-of-said bubble and/or level is accurately determined and'indicated byelectric or electronic circuitsand instruments.

"Conventionallevels, such as are used by engineers, surveyors, and 'the like, and'also simple levels 'such'as are used'by carpenters, brick layers =arid'the like, have vials or tubes usually '"fQrmedpf -gIa'ss and containing a liquid-therein. *Thereis 'usually-suificient' liquid in the vial to provide a gas gubble of substantially desired volume whereby when the vial is inlevel position the extremities or ends of the gas-bubble are substantially inalignment with lines or calibrations on the vial. The user can adjust the instrument whereby the position of the'bubble is 'such' 'that 'it indicates approximately level. tOn engineers levels the vial is usually placed vunder the telescope and the user must stand at the side of the in'strumentand manipulate the'levcling screws until -the bubble appears to be centered' relative to the calibrations, but when the user looksathroughithe telescope merely 'moving 'around' the device or. placing his hand on the 1 support or other parts of the devicecanimove same from level position contributing 'to' errors in reading as Well as considerable .timeinimoving from one position to another to .check the level an'd make the sight.

The objects of the present invention: are to provide a tube having liquidttherein and elecwtrically operated apparatus for indicating "the "location of 'the'liquid level; to providean instru- ..ment'having.a vial of. liquid witha" bubble there- .in'andelectrically operated apparatus to .determine the location .of" the bubble and indicate "whenxsaid position is within desired limits of level. condition; 'to provide apparatus .for determiningr position of:r.a bubble in avial and indi- -:;cating said position ona'meter remote from said ivial toxprovide apparatus for electronically de- .terminingi relative". movement :of a bubblein a vialiforzindicatingthe angular movement ofsaid vial; to provide a'meterioperable in responseto :change. in balanceitofan electric circuit effected ibyimovement of the bubble' to indicate relative position or movement-of saidbubbleytoxprovide ;..a: meter "in 1.3...11818500136 of a level with :a .wire' or 'rhairimovable' in response to .changerof positionrof ithetbubble-ato ialignuwith the cross.;hair: or other index lines of :said telescope when said i bubble is in level position; whereby the level indicating device is in the sight:ofthe;user looking through said telescope; to provide-apparatus '1 for Telectronically determiningand indicating the 'level position of a bubble era-level instrument-and permit inversion 30f *said instrument; to "provide an electronic" circuit with an indicator of variable sensitivity' for determining and indicating when the bubble Within certain limits 'of level position for fastreading ofz'desirediiaccuracy; and

to provide a levelin'strumentwitha" head having detachable electric connections for "supplying current from -a-source on the tripod to the electronic instrumentfor'determining and indicating 'the position ofthe bubble in' a-vial adjustably carried on the telescope.

In accomplishing these and other objects of the present invention,'"Ihave provided improved details of structure, the preferred forms of which are illustrated in the accompanying drawings, wherein:

Fig. 1 is a perspective view of an engineer's level and tripod, said level embodying the'features of the present invention.

Fig. 2 is a side "elevation of thelevel head and telescope.

Fig.3 is a transverse sectional view through the level head on'the'line 3-3,'Fig. 2, said head being illustrated as being mounted on a base adapted to be threaded on atripod.

Fig. 4 is a longitudinal sectional view through the level vial, particularly illustrating the position of the electrodes therein.

Fig. 5 is a transverse sectional viewthrough the telescope, particularly illustratingthe level indicating hair and the cross" hairs 'in' the telescope.

Fig. 6 is awiring diagram of'the electronic apparatus for determining'the position of the bubble.

Fig. 7 is a modified form'of'level vial and electrodes.

Fig. 8 is a transverse sectional View through 'Fig. 9 is a diagrammatic view of an angle measuring device" with control.

Fig. 10 isa-side elevation of another form of angle -measuring :device.

Fig. 11 is a diagrammatic view'of: an electronic apparatus'for determining the location of v the tion of'which is-idescribed: for -the purpose of illustration as representing an example of an instrument to which my invention may be applied. The engineers level includes a telescope 2 mounted in spaced bearings 3 for rotation about an axis coinciding with the line of sight of said telescope. The spaced bearings 3 preferably include a latch 4 for securing the telescope in selected position and preventing rotation of same in the bearings. The hearings 3 are preferably arranged at opposite ends of a bar 5, one end of which is pivotally mounted as at 6 to an upper plate I secured as at 8 on the upper end of a spindle 9. The opposite ends l9 and H of the bar and plate 1 respectively are provided with adjusting screw assembly l2 opposite the hinge 6 whereby turning of the screw tilts the bar 5 and telescope 2 relative to the plate I. The spindle 9 is rotatably mounted on antifriction or other suitable bearings l3 in a leveling head M.

The leveling head is supported on a foot plate l5 by a plurality of leveling screws it for adjusttion of the upper plate for controlling the rotation of the spindle 9 relative to the leveling head I4 as in conventional practice. The foot plate i5 is provided with an internally threaded depending flange l9 threaded onto the upper member 20 of a tripod 2| to secure the instruments thereto, said tripod having legs 22 pivotally mounted as at 23 on said upper member 20. as in conventional practice.

A casing 24 is suitably fixed relative to the telescope 2 for movement therewith, this casing preferably being water and dustproof. The casing is illustrated as being mounted on the side of the wall 25 of the telescope and is hollow to receive a level vial 26 which is of elongated tubular structure preferably formed of glass or other suitable non-conductor of electricity. The relative shape of the casing 24 and vial 2G is such that the walls thereof are spaced as at 21. The ends of the vial are closed as at 28 and are preferably mounted in blocks 29 having threaded bores 39 adapted to receive the shanks 3! of adjusting screws 32, the shanks 3| extending through apertures 33 in the wall of the casing 24 whereby rotation of the screws 32 adjusts the position of the vial relative to the casing to parallel relationship with the line of sight of the telescope 2. Use of two screws 32 at each end of the vial provides a structure which looks the vial in adjusted position.

The vial 2B is filled with a suitable liquid 34 to provide a gas bubble 35 whereby said gas bubble will move in the vial in response to tilting movement of the telescope and will be centrally positioned when the telescope and vial are in level position. In the structure illustrated in Fig. 4 there are partitions 36 spaced from the closed ends 28 of the vial, said partitions preferably being formed of insulating material. Supported in the partitions coaxial with the walls of the vial is an electrode 31, the ends of said electrode extending through and being supported by the partitions 36 and rigidly secured thereto by suitable fastening means 38, one end of said electrode 31 being connected to a conductor 39 which extends through the adjacent closed end of the vial and is connected to a suitable ground of a cir- 4 l cuit later to be described. Suitably mounted on the partitions above the electrode 37 and substantially in a vertical plane therewith are electrodes 49 and 4|, said electrodes preferably being in contact with the walls of the vial and extending from each of the partitions 38 toward the longitudinal center of said vial, said electrodes terminating as at 42 whereby the spacing between the adjacent ends of said electrodes is of less length than the length of the gas bubble 35, as illustrated in Fig. 4. Identical electrodes 40' and 41 are mounted on the partitions below the electrode 31 in vertical alignment therewith, the spacing of the electrodes 49 and 41' and the spacing from the electrode 31 being substantially the same as the corresponding spacing of electrodes 40 and 4|.

The electrodes 40 and 40' are suitably connected in parallel circuit with a conductor 43 and the electrodes 4! and 4| connected in parallel circuit with a conductor 44, said conductors extending through the closed ends 28 of the vial for connection in an electric circuit as later described. The conductors 39, 43 and 44 are preferably enclosed in a cable or otherwise suitably insulated from the metallic members of the instrument, said cables preferably being enclosed by a conduit 45 leading to a housing 46 which encloses a variable resistance 41, variable condenser 48, a transformer 49 and other electrical equipment later described in connection with the electric circuit. The housing 46 is illustrated as being suitably mounted on the opposite side of the telescope to the casing 24. However, said housing may be positioned anywhere on the instrument to provide for convenient access to control knobs or the like 50 and 5| ar-- ranged exteriorly of said housing and having suitable connection with the variable resistance 41 and variable condenser 48 respectively for adjusting same.

The telescope 2 is tubular as in conventional structures and has a conventional frame 52 therein secured to the wall 25, said frame supporting the usual horizontal and vertical cross hairs 53 and 54 respectively whereby the point of intersection of said hairs is in the line of sight from the eye piece 55 of said telescope. A suitable meter 56 may be arranged at any location remote from the vial, but in the illustrated engineer's level is enclosed in the telescope and secured to the wall 25 thereof adjacent the frame 52, said meter having electromagnets 51 energized by the electric circuit for rotating an armature 58. An arm 59 is fixed to the armature 58 and extends therefrom terminating as at 60 on the opposite side of the line of sight of the telescope. The intermediate portion 6| of the arm is preferably arcuate in shape whereby a cross hair 62 secured to the portion of the arm adjacent the armature extends in a straight line across the line of sight of said telescope and is secured to the end 69. The curvature of the arm 59 is such that when the cross hair 52 aligns with the cross hair 53 the intermediate portion 6! of said arm is out of the area visible to the person sighting through the telescope but is small enough that when the arm is moved from horizontal alignment with the cross hair 53, as illustrated in Fig. 5, there is sufiicient clearance between the arm 59 and the wall 25.

The conductors leading from the power supply and to the housing 46 are preferably enclosed in a cable 63 which extends through a bore 64 in an insulating tube 65 suitably secured in the spindle 9, the upper end of the tube 65 preferably having a rubber or like bushing 66 to protect the -=cable-from=the edges 'ofsaidtube. The: insulating tube is illustrated as extendingthrough an aperture '61 in -the bar-5 and anape'rture' -G8 in the upper plate 1 to protect the cablefrom-wear'by contact with the other members or the instrument during use; The cable and the conductors-therein lead Y to" suitable-"A batteries 60 and- B :batteries enclosed ina suitablehousing 12 :locatedon' the apparatus-for convenience in carrying/said housing preferably being mountedas at 13@on oneof.

the legs 22 of thetripodaslillustrated in Fig; 1. A suitable connection between the portions: of

Ii the cable is providedtopermit the-easy removal of the foot plate :15 :from. the :upperir end, of. the

tripod. The: connectionconsists fofJ mialesfand 1 female memberstl l and 15,-. one" being connected -to thecable leading ifrom .the batteries .andthe otherab'eing mountedonr'the levelinglhead. :;=It is also desirable thattthe' electricalconnections: do

-not interfere-with relative rotation or the :spindle-j;

9. and leveling head I 4. Thereforentherinsulating .t ube'65 terminates atiitsllower: endfin. ablocklfi of 'insulatingimaterial. having .contacts 11 and 18 1 arranged at different radial" distances. from the .axis of rotation .of .the spindle .0, said: contacts being electrically connected to .the conductors in the cable 63. The contacts "and 18 havesliding engagementwith conductor rings. 19 and 80 respectively mounted-yin insulating material: 'ofzthe connector member. 15; said rings; having electric connection through the members 14 and '15. to 'rthe conductors; leading .to the batteries when the a members 14 and ;15;are. engaged. The; member 15 :isrprovidedwith: ari flange; 8 lyrengaged by. aminturnedxflange; .82; onga gnut 83-.threadedl secured .toza depending a tubular wall-.- 84 on the "leveling Ahead 14 whereby the nut'83; retains the rings 19 and 80 in engagement with r the contacts "and '18. The member 15 .is.:illustrated .ashaving a conductor 85in electrical contact with the nut 83 and-connected through the :members 14-15 and cable to the groundterminals of the batteries whereby the; ground connection of the electrode 31 and from electrical apparatus in the housing may be connected to themetallic members of the telescope to .form a complete circuit. However, athird ring and contactwitn suitable conductors'could-be arranged to completethe circuit without grounding same to any portion of the instrument.

The electrical.apparatusillustrated in Fig. 6 consists primarily of .an impedance-.measuring circuit such as abridge.circuit;86:having a suitable source of electrical energywhereby the meter 56 or null indicator indicates when the bridge icircuitis in balanced: condition. the armature arm-5Q moving to position, the crossi hair. 62; in alignment witnthev cross hair- 53 whensuch balancedcondition'is obtained, thG'ICIOSS hairs beingout of alignment when ,thebridgecircuit is not in balance. However, other circuits may be used that will compare .or measure relativeimped- ,ance or capacitance in portions of a vial of liquid to indicate.accurately-the position of the-bubble therein. ;A suitable arrangement .for. .supplying electrical energy to the bridge; circuit. :is .illustrated in Big... 6, wherein. an ioscillatoncircuit: 01 is inductively coupled. bym'eans -.0f.ithe: transformer '49 with the-bridge circuitfifipsaid transformer having awinding 88 in the oscillator 'cir-*- cuit, and a winding 89 ingthe bridge circuit. The B battery-10 has oneside suitably-groundednas at 90..and is 'connectediby. a: conductor. 9|; with a center tap 92 on winding 08; the ends. 'DfL'Said -winding. being, connected .by. conductors 93 sand 194K150 supply currentrztoi the-iplates-"ili and =1 96:: of ea twinsntriodeitubei 91. Therconductor." 9|: has a I' connectioniwith aircondenser 9,8,- .ithe other? side 1: of' whichis: grounded. The A battery'liil'. has," one 5 side connected by a conductor."99' 'withthe filar-iment;- |00;.;of= thetriodetube. The other side of ;the :battery' .69 is: connected tby azcondu'ctor" l 0 l fwitlr lthet; filament" I 00, said conductor i 10 I? also being-:zprovided' with a" :ground connec'tiont "I 02. 10: Connected- With".th6' conductor I0 I are" conductors "I03 'and'lflkhaving resistances I05 andlOB respectitelyrarid connected: to "grids? I01 and I08 respectively. .Also =connected: to the gridsuare :conductors: I09.- and. H 0 which" are connected by 15 :taps lll cand' l'i'l2ewithf.the' coi1=:88, said-conducitors having condensers H 3 and H 4" respectively :Ltherein.

Y The. oscillator: circuit arrangedv as described infdllCBSiEtl'l' alternating current. of suitable voltage 530 in the "coil 89 of :the" transformer 49;.the ends of said "coil 39 being connected to conductors H5 "and IIS'respectively, saidconductor H5 being "connected to: the bridge. circuit 86 between arms H1 and H8 andthe conductor I I6 between arms i H9 and I20. vThe arm ill of: the bridgezcircuit 'ihas a condenser 12! of'fixedpapacity, and the arm- N9" the variable condenser 40. The .electrodesM and'31 .with:the dielectricliquid in the levelvial. form a: condenser :in the arm Hlland the electrodes and 31 with the dielectric liquid of the" vial. iormca condenser. in: the 1 arm I20. :The: electrode 31 'is' connected through a rectifier crystal .I22rto oneside of the vmeter 56,'ithe other side of: said meter beingconnectedbetweenthe Smarms H Srand I11. Ascoil l23r'has one'side connected hetweenrthe arms H1" and H9 and the other side groundedas at I 24. Connected around the meter. is a condenser I25: and also connected 1 around the; meterxis .thervariable resistance 41, lo-said variable resistance serving as a volume control to vary'ithe sensitivityofthe meter. The suseof the 5 two electrodes 40 and' iil connected parallel in "theiibridgearm l20pand'the two .xelectrodes 4| aandt'4l. in'parallel in the bridge arm I I8 with each electrode of each pair in verticaLalignmentzwith the electrode '31 permits op eration of the instrument witheither side of the :level vial up, thereby.permitting'inverting of the instrument. In' other words, the telescope may .be rotated .in the bearings 3. throughanarc of .180 degrees providing checkas to the align- =-ment of the 'vial with the line of sight of'the telescope. Small misalignment maybe com- ;rpensated by. adjusting the variable condenser J 48 by means of kn'ob 5l to bring the cross hair into coinciding relation-with the cross hair 53 in both mpositions of thetelescope'in the inverting of same.

"Tilting of the :vial '26 will effect movement of the -gas bubble '35. For example, if the eye piece portion Ofthetelescope is lower than the :opposite end, the bubbleflfi "willmove toward athe electrode '40 z efiecting a change bin-position of-theliqui'cl and airand since the dielectric constant of the air or-gas is. small, approximately :":unity,-:and the'dielectric constant of the liquid iii greater 1 than unity, the impedence between the electrode 40- and' the=electrode 3'? will bei. 'come' less thanthe impedance betweenthe elecxtrodetM .andztheelectrodetl, elfectingan un ibalanced condition-fin the bridge circuit. Mov- :zingLthetelescope by means of adjustment of .ztherleveling screws 16 to bring the bubbleback 2:170 .the position .shownin Fig-"4, whereby the same .:proportions ofIi-the electrodessdil and "4 l= extend into the bubble, will effect a balanced condition in the bridge circuit. As the bridge circuit becomes balanced the armature 53 rotates to move the cross hair 62 into position to coincide with the cross hair 53.

In using an engineers level constructed as duc'tors leading from the batteries'to the oscilladescribed, the tripod with the batteries in the case I2 on one of the legs is set up and the foot plate I screwed onto the top member 20 of said tripod. The connecting member I4 is connected with the member I5 to complete the circuit from the batteries to the rings I9 and 80 and ground connection 85 whereby the electrical circuit is connected through the contacts I! and I8 and the metal portions of the leveling head to energize the oscillator circuit and induce the flow of alternating current to the bridge circuit 85. The instrument is then set up in the desired location with the legs of the tripod spread to firmly support the level. The leveling screws I6 are then manipulated while the user observes the spirit vial II to form a rapid approximation of level condition of the leveling head and vertical arrangement of the spindle 9. The user then looks through the telescope toward the target and manipulates the adjusting knob I2'I to focus the telescope thereon. Then by further adjustment of the leveling screws IE, or for some work adjustment of the screw assembly I2, the telescope is tilted to bring the bubble 35 to level position as illustrated in Fig. 4. As the bubble approaches the level position the irnpedances between the electrodes 40 and 31, and II and 3'! operate with the capacities of the condensers 48 and I'll to effect a predetermined relationship in the arms of the bridge circuit. The meter 56 indicates when the balanced condition or null point occurs by moving the armature 58 to align the cross hair 62 with the cross hair 53. Turning the knob 50 to adjust the variable resistance 41 varies the sensitivity of the meter 51 whereby, if desired, the sensitivity of the level is less than the pointing power or accuracy with which the telescope can be resighted in the same direction to the same point, it being possible to secure a sensitivity of less than one-fourth of a second of angular measurement. However, the sensitivity can be adjusted according to the work being done. For example, the resistance 4I- may be set whereby the meter indicates a balanced condition within limits of twenty seconds variation, then the adjustments of the leveling screws can be made more rapidly than the fine adjustments required for a low sensitivity. Therefore, the instrument may be adjusted to accommodate it for fast reading of suflicient accuracy for some work or can be adjusted to read with the greatest accuracy necessary.

The alignment of the axis of the vial 26 with the line of sight of the telescope may be checked by inverting the instrument, that is by rotating the telescope through an arc of 180 degrees thereby positioning the vial on the opposite side of the telescope and utilizing the electrodes 40' and 4! on the opposite side of the vial. This arrangement of the vial operates in exactly the I same manner and if there is any misalignment the screws 32 may be adjusted to position the vial in proper alignment or the variable condenser 48 may be adjusted to actuate the null indicator at the desired relative impedance or bubble position. Also the telescope may be turned in the opposite direction, that is around a vertical axis by rotating the spindle 9 to check said vertical axis, said rotation not interfering with the conrotate on the rings I9 and to maintain the electrical circuit. v

With the vial constructed as illustrated in Fig. 4, an ordinary direct current bridge circuit may be used if a liquid 34 having the proper D. C. impedance characteristics is used.

In the modified form a vial illustrated in Figs. 7 and 8, a vial I28 of glass or other material is substantially filled with liquid I29 to form a gas bubble I30 therein. Suitably secured on the vial in engagement with the exterior surface thereof and adjacent the ends are electrodes I3I and I 32, the electrodes at like ends being connected in parallel in the same manner as the electrodes 40-40 and 4I'-4I. The inner ends of the electrodes I3I and I32 extend toward the longitudinal center of the vial terminating as at I33 in spaced relation, said space being less than the length of the bubble I30. Extending for the full length of the vial and on diametrically opposite sides thereof and equally spaced from electrodes I3I and I32 are electrodes I34 whereby the glass or other material of the vial and the liquid combine to form the dielectric to provide the capacity at each end of the vial.

In using a vial constructed as described, electrodes I3I are connected in the bridge circuit in the same manner as the electrodes 40 and 40' and electrodes I32 connected in the same manner as the electrodes II and 4|. The electrodes I34 are connected in the same manner of the electrodes In this arrangement the operation is substantially the same and the instrument may be inverted as the various electrodes are in duplicate in the same manner as described in connection with the circuit in Fig. 6.

In the form of the invention illustrated in Fig. 9 the vial I35 is supported on a housing I36 which encloses the electrical apparatus supplied by current from a suitable source of supply. The electrical circuit may be similar to that illustrated in Fig. 6 or other suitable circuit to energize a meter I31 graduated in increments of angular measurement whereby when the housing I36 is mounted on a support I38, the angle of slope of said support may be measured. The instrument may also be used to control the level of a support by use of a suitable transformer having a winding I39 in parallel circuit with the meter and a secondary coil I40 connected to a suitable electrical circuit including relays, motors and the like for raising and lowering the support to maintain same in level condition.

In the form of the invention illustrated in Fig. 10, the telescope or other device I4I has trunnions I42 rotatably mounted in suitable bearings I43 carried on a frame I44. Fixed to the trunnion is an arm I45 having graduations I46 adapted to coincide with graduations I47 of a semicircular member I48, the graduations I46 serving as a vernier and being in increments of angular measurement whereby the angle of tilt of the telescope I4I may be measured. The level vial is supported in a housing I49 rotatable about the trunnion I 42, a clamping device I50 being provided to lock the level in its correct position relative to the trunnion. The level vial is of the same construction as illustrated in Fig. 4 or Fig. 7 and has a conduit I5I leading to a suitable electric circuit having a power supply and a meter I52, said meter being graduated in increments of angular measurement whereby tilting of the vial will be indicated thereon. With this arrangement the telescope ,I 41 may ,be rotated; througha sub:

stantially I desired angle. .indicated by. the. gradue ations I46 and I 41 The.clamping. -device :I 5011s..

loosened and the level vial rotated until the hand I53 of the meter is at zero. That indicates that the level. vial is ,level. Then. by. tightening the, screws of the .clampISi], any furthenangular,

with so.that. the .liquid.'I56 'will'rise. or lower the .bore II oflthe tube in accordance .with the elevation of said liquid body. Supported in the. tube and preferably coaxial therewithiis' an electrode. I58 which extendsintothe liquid in the tube.. A plurality of electrodes I59, I60, I6I, 162" and I63 are mounted on the tube in contact with the walls thereof, said ,electrodes being spaced and in staggered relation around the tube so ad-i jacent end edges of the electrodes overlap but'do'. not contact. The electrodes I59,I66;I6I, I62 and I63 are electrically connected to'contacts'I'59,

I60, IEI", I62 and-'I63"respectively of a com-- mutator switch l64g the arm I65 of which is c0nnected in a legr'l66 of'asuitable-bridge orother impedance measuring circuiv'l61;. The electrode I58 is also 'connected-inthe same leg I66 0f "the circuit I61 whereby said "electrode I58 "and the electrodes I59; I60; ISI; I62; and-463 with -the liquid I56 therebetween form theimpedance to be measured.

The circuit I 61 -similar-to--the circuit 86' and receives electriccurrent from i a suitable source l of supply'connectedto conductors-I68 :and 'l69,

which current actuates-a-meter II min accordance with variation in the impedance of'theliquid and:

gas between the electrodes. of the'tube I55 .in..re-

lation to the 'capacitiesof condenser Ill :and; variable condensers .I I2. and;.I'I3 .1in'..other:-1egs;,ofthe circuit I671; The meter I'IB preferablyis cali:

bratedin units. of linear measurement.

In using apparatus constructed andconnected as described, the'current is .suppliedtothescircuit. IB'I, then the commutator switch. armil65'isc moved to engage contact I59 and ifthe elevation of liquid is above the upper edgevofithe electrode I59 the meter will be actuated to showthe liquid elevation is at or above the upper. limit of the par! tition of the tube adjacent the electrode I59... The...

arm I65 is then movedto contact .I6.Il and the switch is preferably marked to indicate the height of liquid at the lowerend of electrode, I60. The. meter will again show that the liquidelevation i1-'- lustrated is above the upper edg'eof the electrode in the circuit. The arm I65 is then moved to. contact I6I' which places the electrodes I6I and I58 in the leg of the circuit 'I6I,"and the meter" will indicate the height of the liquid by the rela tive impedance between the electrodes I6I and I58 and the other'legs ofthecircuit which'will' be determined according to the impedance of'tlie portion of the tube having liquid and the portion having gas between the electrodes I6I and- I58;

The meter being calibrated in units of linear. measurement will showthe height of the liquid 1 above the lower edge of the electrode I6I which 1.

length is added to the height; shown by thenpo-J sition of the arm I65 to give the total height of the liquid elevation in the body of liquid being measured. Obviously the meter and switch couldi be calibrated in gallons or other liquid measure.

if 1 desired.

Iha-ve illustrated and described..the..electron1ca level in connection with. an. engineerfsf, level fandi angular. measurement devices, however, it' islbee, iieved obvious that ,the,.electrical jcir'cuitfand the level -.vial may b'eused inany instrument iorde-q termining level conditions.accurately, for. ex: ampl, even in a carpenters". level.

It. is...believed that I'ihave .provided' an elec-.. tronic. level .wherein the location of the bubble and/ or liquid elevation is indicated by; movement-l of an. arm ofta meter whereby said indication may, be remote from the levellvial .toprovide' accurate, fast. readings. Also I have arranged suchlameter inthe telescope of an .engineers level orthe like 1 device wherein the level position may be read-att the same time as making the .sight..

What lclaim and desireto secure .by littersa Patentis:

1. Apparatus for. determiningthe position .of a. bubble in confined liquidcomprising-a .vial haying liquid therein forming-a bubble which is -.cen.-,. trally located-when said vial is leveland movable;- from said central locationwhen the .vialis tilted-,1. spaced. pairs ofelectrodes .oppositelydisposei relative to the level position of the bubblerandl having .adj acent ends overlapping opposite edges,.; of said bubble, the liquid being between .theelec-htrodes of each pair, a common electrodeabetweenc and equallyspaced from theelectrodes .of each pair, an electric circuit connected to thencommonuelectrode and pairs of electrodes;whereby move- 1 .-v ment.of:.the bubble variesqthe impedance-'in'gthea circuit, and means formeasuring. the-avariationg; inimpedance in the :electric circuit for indicating extent-.of movement of the bubble in-the vial'sand accuracy or indication, on inversion of the :vial;

2. cA level of the: character; described comprise; ing. an elongated-vial. liquid in the vial"and.-form.-. ing. a bubble which is centrally locatedy therein when said vial-is level-and movable from;sa -id v position. when :the vial-is tilted; 1spaced--v pairs. oft electrodes respectively aligned and having adja-w cent portions overlapping. opposite ends of ;the..- bubble when the-vial is in level position-ea com-@- mon electrode spaced fromtheelectrodeslofeaclhg; pair and: arranged parallel. therewith withathev liquid therebetweenwhereby; I movement; of the.- bubble variesthe impedance between the-respecg tive aligned electrodes and "said 'commoncelec trode,-a bridgecircuit, means connecting one. of;- the pairsofelectrodes and the common ,electrode-. in one arm-of the bridgecircuit and the;-other-,-= pair: of electrodes and said common electrode-mg; an adjacent arm of said bridge circuit, a 'null in-w dicator in the bridge circuit; means supplying alternating, current to the bridge circuit for .ac-,-- tuating the null indicator :to .indicate when the. bubble isin leveLposi-tionand means-in one-of the arms of the bridge circuit'for adjustinggthe nullypoint of the circuit relative to the position-oi: the bubble. I

3. A level of the character described,- compris ing,.. an elongated vial, liquid in the vialvand: forming. a bubble which is centrally located; therein when said .vial is level: and movablefrom said position when the. vial -istilted,-. saidliquid having a dielectricconstant greater than .unity, spaced pairs of electrodes respectively aligned..- andhaving adjacent portions overlappingopposite. endsof the bubble when .thevial. is inlevel position, a;.common electrode spaced. from the.- electrodes. of each pair and. arranged parallel therewith with the. liquid'as a dielectric there betweenwhereby movement of the bubble varies the capacitance between the respective aligned electrodes and said common electrode, a bridge circuit, means connecting one of the pairs of electrodes and the common electrode in one arm of the bridge circuit and the other pair of electrodes and said common electrode in an adjacent arm of said bridge circuit, a null indicator in the bridge circuit, means supplying alternating current to the bridge circuit for actuating the null indicator to indicate when the bubble is in level position, and means for varying the sensitivity of the null indicator.

4. A level of the character described comprising, a telescope having cross hairs therein, means for leveling said telescope, an elongated vial adjustably mounted on said telescope parallel to the line of sight thereof, liquid in the vial and forming a bubble centrally located therein when the vial is level and movable from said location when the vial is tilted, an electric circuit, means in said circuit responsive to movement of the bubble in the vial for indicating the relative position of said bubble, and an arm in the telescope and operable by said indicating means to align with the cross hair of said telescope when the bubble is in level position, whereby the level condition is indicated in the telescope while a sight is being made therewith.

5. A level of the character described comprising, a telescope, means for leveling said telescope, an elongated vial adjustably mounted on said telescope parallel to the line of sight thereof, liquid in the vial and forming a bubble which is centrally located therein when the vial is level and movable from said location when the vial is tilted, spaced pairs of elongated electrodes longitudinally of the vial oppositely disposed relative to the level position of the bubble and having adjacent ends overlapping opposite ends of said bubble, the liquid being between the electrodes of each pair, a central elongated electrode equally spaced from and parallel with each electrode of each pair, an electric circuit connected to the central and pairs of electrodes whereby movement of the bubble varies the impedance in the circuit, the electrodes of each pair being in parallel circuit, means for measuring the variation in impedance in the electric circuit for indicating when the bubble is in level position, and means rotatably mounting the telescope for inverting same and the vial thereon whereby the impedance variation measuring means will indicate the parallel relationship of the vial to the line of sight of the telescope.

6. A level of the character described comprising, a telescope having cross hairs therein, means for leveling said telescope, an elongated vial adjustably mounted on said telescope parallel to the line of sight thereof, liquid in the vial and forming a bubble which is centrally located therein when the vial is level and movable from said position when the vial is tilted, a bridge circuit, an indicator connected in the bridge circuit for indicating null point between the arms of said bridge circuit, an arm having a cross hair extending across the line of sight of the telescope and operable by the indicator to position said cross hair in horizontal alignment with the horizontal cross hair of the telescope only at the null point of the bridge circuit, means connected in adjacent arms of said bridge circuit, and on op posite sides of the level position of the bubble whereby movement of the bubble varies the impedance in the respective arms of the bridge cir- 1'2 cuit, and means in one arm of the bridge circuit for adjusting the null point of the circuit to correspond to the impedance therein when the bubble is in level position.

7. A level of the character described comprising, a telescope having cross hairs therein, means for levelling said telescope, an elongated vial mounted on said telescope parallel to the line of sight thereof, liquid in the vial and forming a bubble which is centrally located therein when the vial is level and movable from said location when the vial is tilted, a bridge circuit connected to a source of electric energy, an indicator connected in the bridge circuit for indicating balance between arms of said bridge circuit, said indicator being mounted inside of the telescope adjacent the cross hairs thereof, an arm having a cross hair extending across the line of sight of the telescope and operated by the indicator to position said cross hair in horizontal alignment with the horizontal cross hair of the telescope when the bridge circuit is balanced and move the arm to disalign the cross hairs when the bridge is unbalanced, aligned electrodes having adjacent portions overlapping the opposite ends of the bubble when the vial is in level position, a common electrode spaced from the aligned electrodes and arranged substantially parallel therewith with the liquid forming an impedance therebetween whereby movement of the bubble varies the impedance between the respective aligned electrodes and the common electrode, and means connecting one of the aligned electrodes and the common electrode in one arm of the bridge circuit and the other aligned electrode and said common electrode in an adjacent arm of said circuit, whereby central location of said bubble efiects a balanced condition in said bridge circuit.

8. A level of the character described comprising, a telescope having cross hairs therein, means for leveling said telescope, an elongated vial adjustably mounted on said telescope parallel to the line of sight thereof, liquid in the vial and forming a bubble which is centrally located therein when the vial is level and movable from said location when the vial is tilted, said liquid having a dielectric constant greater than unity. a bridge circuit, a null indicator connected in the bridge circuit for indicating balance between arms of said bridge circuit, said indicator being mounted inside of the telescope adjacent the cross hairs thereof, an arm having a cross hair extending across the line of sight of the telescope and operated by the null indicator to position said cross hair in horizontal alignment with the horizontal cross hair of the telescope when the bridge circuit is balanced and move the arm to disalign the cross hairs when the bridge is unbalanced, batteries for supplying current, an oscillator circuit energized by the batteries for deliverin alternating current to the bridge circuit, aligned electrodes having adjacent portions overlapping the opposite ends of the bubble when the vial is in level position, a common electrode spaced from the aligned electrodes and arranged substantially parallel therewith with the liquid as a dielectric therebetween whereby movement of the bubble varies the capacity between the respective aligned electrodes and the common electrode, means connecting one of the aligned electrodes and the common electrode in one arm of the bridge circuit and the other aligned elec trode and said common electrode in an adjacent 13 14 arm of said circuit, whereby central location of UNITED STATES PATENTS said bubble efiects a balanced condition in said Number Name Date bridge circuit, and means for varying the sensi 2,041,526 Carter May 19, 1936 of the null indicamr- 2,252,727 Pepper Aug. 19, 1941 5 2,350,240 Leister et a1. May 30, 1944 WILLIAM MOORE- 2,367,465 Munzer Jan. 16, 1945 REFERENCES CITED FOREIGN PATENTS The following references are of record in the Number Country Date file thls Paten 148,635 Great Britain July 29, 1920 

